http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/RSS.ashxRA PagesWed, 12 Sep 2007 07:50:13 +0200http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=1http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=1REFRIGERATION AIR CONDITIONING DIVISION CO2 refrigerantfor Industrial Refrigeration Article MAKING MODERN LIVING POSSIBLE2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=2http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=22007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=3http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=3RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 3 Article CO2 refrigerant for industrial refrigeration Contents Page Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Characteristics of CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 CO2 as a refrigerant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 CO2 as a refrigerant in industrial systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Design pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Eciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Oil in CO2 systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Comparison of component requirements in CO2, ammonia and R134a systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Water in CO2 Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Chemical reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Water in Vapor Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=4http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=44 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration The application of carbon dioxide CO2 in refrigeration systems is not new. Carbon dioxide was rst proposed as a refrigerant by Alexander Twining ref. 1, who mentioned it in his British patent in 1850. Thaddeus S. C. Lowe experimented with CO2 military balloons, but he also designed an ice machine with CO2 in 1867. Lowe also developed a machine onboard a ship for transportation of frozen meat. From reading the literature it can be seen that CO2 refrigerant systems were developed during the following years and they were at their peak in the 1920s and early 1930s. CO2 was generally the preferred choice for use in the shipping industries because it was neither toxic nor ammable, whilst ammonia NH3 or R717 was more common in industrial applications ref. 2. CO2 disappeared from the market, mainly because the new wonder working refrigerant Freon had come on the market, and was very successful in marketing this. Ammonia has continued to be the dominant refrigerant for industrial refrigeration applications over the years. In the 1990s there was renewed focus of the advantages oered by using CO2, due to ODP Ozone Depletion Potential and GWP Global Warming Potential, which has restricted the use of CFCs and HFCs and restrictions on the refrigerant charge in large ammonia systems. CO2 belongs to the socalled Natural refrigerants, together with e. g. ammonia, hydrocarbons such as propane and butane, and water. All of these refrigerants have their respective disadvantages Introduction Ammonia is toxic, hydrocarbons are ammable, and water has limited application possibilities. In comparison, CO2 is nontoxic and nonammable. CO2 diers from other common refrigerants in many aspects, and has some unique properties. Technical developments since 1920 have removed many of the barriers to using CO2, but users must still be highly aware of its unique properties, and take the necessary precautions to avoid problems in their refrigeration systems. The chart in gure 1 shows the pressure temperature relationship for CO2, R134a and ammonia. Highlights of CO2s properties relative to the other refrigerants include Higher operating pressure for a given temperature Narrower range of operating temperatures Triple point at a much higher pressure Critical point at a very low temperature. While the triple point and critical point are normally not important for common refrigerants, CO2 is dierent. The triple point is high 5. 2 bar 75. 1 psi, but more importantly, it is higher than the normal atmospheric pressure. This circumstance can create some problems, unless the proper precautions are taken. Also, CO2s critical point for is very low 31. 1C 88. 0F, which greatly aects the design requirements. In table 1, the dierent properties of CO2 are compared with R134a and ammonia. Figure 1 Pressure Temperature 0, 001 0, 01 0, 1 1 10 100 1000 12060060120180 Temperature Pressure bar Pressure psi bar 14500 1000 145 10 1. 45 0. 1 0. 015 0. 001 120 60 0 60 120 180 o C 184 76 32 140 248 356 o F Temperature CO2R717 R134a Triplepoint Criticalpoint CO2 properties compared with various refrigerants Refrigerant R 134a NH3CO2 Natural substance NOYESYES Ozone Depletion Potential ODP000 Global Warming Potential GWP13001 Critical point bar psi C F 40. 7 590 101. 2 214 113 1640 132. 4 270 73. 6 1067 31. 1 87. 9 Triple point bar psi C F 0. 004 0. 06 103 153 0. 06 0. 87 77. 7 108 5. 18 75. 1 56. 6 69. 9 Flammable or explosive NOYESNO Toxic NOYESNO Table 1 pr EN 3781 2003 Author Niels P. Vestergaard R D Manager Danfoss Industrial Refrigeration2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=5http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=5RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 5 Article CO2 refrigerant for industrial refrigeration 40 20 0 20 40 o C 40 4 32 68 104 o F Saturated temperature 40 20 0 20 40 o C 40 4 32 68 104 o F Saturated temperature Density 93. 61500 62. 41000 31. 2500 00 Liquid Vapour Criticalpoint 31 o C 87. 9 o F 73. 6 bar 1067 psi Lbft3kgm3 Density CO Liquid Vapour2 Figure 2 shows the temperaturepressure phase diagram of pure CO2. The areas between the curves dene the limits of temperature and pressure at which dierent phases can exist solid, liquid, vapor and supercritical. Points on these curves indicate the pressure and corresponding temperatures under which two dierent phases can exist in equilibrium, e. g. , solid and vapor, liquid and vapor, solid and liquid. At atmospheric pressure CO2 can exist only as a solid or vapor. Characteristics of CO2At this pressure, it has no ability to form a liquid below 78. 4C 109. 1F, it is a solid dry ice above this temperature, it sublimates directly to a vapor phase. At 5. 2 bar 75. 1 psi and 56. 6C 69. 9F, CO2 reaches a unique state called the triple point. At this point all 3 phases i. e. , solid, liquid and vapor, exist simultaneously in equilibrium. 1 10 100 1000 80604020020406080100 Temperature Deg. C Pressure bara Liquid Solid Vapour Supercritical CO2Phase diagram Pressure psi bar 14500 1000 1450 100 145 10 14. 5 1 80 40 0 40 80 o C 112 40 32 104 176 o F Temperature o Triplepoint 56. 6C 69. 9F 5. 2 bar 75. 1 psi Criticalpoint Criticalpoint 31 o C 87. 9 o F 73. 6 bar 1067 psi Figure 2 Figure 3 CO2 reaches its critical point at 31. 1C 88. 0F. At this temperature, the density of liquid and vapor states is equal gure 3. Consequently, the distinction between the two phases disappears, and this new phase, the supercritical phase, exists. Pressureenthalpy diagrams are commonly used for refrigeration purposes. The diagram is extended to show the solid and supercritical phases gure 4. The marked areas indicate the dierent phases. 2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=6http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=66 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration CO2 may be employed as a refrigerant in a number of dierent system types, including both subcritical and supercritical. For any type of CO2 system, both the critical point and the triple point must be considered. The classic refrigeration cycle we are all familiar with is subcritical, i. e. , the entire range of temperatures and pressures are below the critical point and above the triple point. A single stage subcritical CO2 system is simple, but it also has disadvantages because of its limited temperature range and high pressure gure 5. CO2 as a refrigerant Transcritical CO2 systems are at present only of interest for small and commercial applications, e. g. , mobile air conditioning, small heat pumps, and supermarket refrigeration, not for industrial systems gure 6. Transcritical systems will not be described further in this handbook. Operating pressures for subcritical cycles are usually in the range 5. 7 to 35 bar 83 to 507 psi corresponding to 55 to 0C 67 to 32F. If the evaporators are defrosted using hot gas, then the operating pressure is approximately 10 bar 145 psi higher. 1 10 100 Pressurebara 1 10 100 Pressurebara 1 10 100 1 10 100 Solid Vapour Liquid Vapour Solid Liquid Log p, h Diagram of CO2 Solid Liquid Supercritical Vapour 78. 4 o C 109. 1 o F Enthalpy Pressure psi bar 1450 100 145 10 14. 5 1 87. 9 o F Criticalpoint 31 o C F 73. 6 bar 1067 psi 69. 9 Triplepoint line 56. 6 o C 69. 9 o F 5. 2 bar 75. 1 psi 101570 43530 72550 130590 735 58040 29020 14510 87060 116080 1450100 101570 43530 72550 130590 735 58040 29020 14510 87060 116080 1450100 bar psi Enthalpy Subcritical Subcritical refrigeration process Pressure 5. 5C 22F 40C 40F Figure 4 Figure 52007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=7http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=7RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 7 Article CO2 refrigerant for industrial refrigeration 101570 43530 72550 130590 735 58040 29020 14510 87060 116080 1450100 101570 43530 72550 130590 735 58040 29020 14510 87060 116080 1450100 bar psi Enthalpy Transcritical refrigeration process Pressure 12C 10F Gas cooling Gas cooling35C 95F 95C 203F Figure 6 CO2 is most commonly applied in cascade or hybrid system designs in industrial refrigeration, because its pressure can be limited to such extent that commercially available components like compressors, controls and valves can be used. Figure 7 shows a low temperature refrigerating system 40C 40o F using CO2 as a phase change refrigerant in a cascade system with ammonia on the highpressure side. CO2 cascade systems can be designed in dierent ways, e. g. , direct expansion systems, pump circulating systems, or CO2 in volatile secondary brine systems, or combinations of these. CO2 as a refrigerant in industrial systems R717 CO2CO2 30C 86F 12 bar 171 psi 20C 4F 1. 9 bar 28 psi 30C 86F 20C 4F 15C 5F 40C 40F Pr essu re Enthalpy Pr essu re Enthalpy CO2 Pr essu re Enthalpy CO2 R717 40C 40F CO2evaporator CO2compressor CO2receiver CO2R717Heat exchanger 15C 5F 23 bar 333 psi 40C 40F 10 bar 135 psi Figure 7 Principal diagram R717 CO2 cascade system CO2 as a refrigerant Continued2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=8http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=88 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration R717 Heat exchanger R717 COCO Pr essu re Pr essu re Enthalpy Enthalpy CO2 R717 8C 46F CO2 CO2 compressor CO2defrost compressor CO2receiver CO2 evaporator 2 30C 86F 20C 4F 15C 5F 40C 40F 40C 40F 30C 86F 12 bar 171 psi 20C 4F 1. 9 bar 28 psi 15C 5F 23 bar 333 psi 40C 40F 10 bar 135 psi 8C 46F 43 bar 633 psi Figure 8 The CO2 system is a pump circulating system where the liquid CO2 is pumped from the receiver to the evaporator, where it is partly evaporated, before it returns to the receiver. The evaporated CO2 is then compressed in a CO2 compressor, and condensed in the CO2NH3 heat exchanger. The heat exchanger acts as an evaporator in the NH3 system. Compared to a traditional ammonia system, the ammonia charge in the above mentioned cascade system can be reduced to approx. 110. Figure. 8 shows the same system as in gure 9, but includes a CO2 hot gas defrosting system. R717 Heat exchanger R717 COCO Pr essu re Pr essu re Enthalpy Enthalpy CO2 R717 CO2 CO2receiver CO2 evaporator 2 30C 86F 45C 49F 40C 40F 40C 40F 40C 40F 30C 86F 12 bar 171 psi 45C 49F 0. 5 bar 7 psi 40C 40F 10 bar 135 psi Figure 9 Principal diagram R717 CO2 cascade system with CO2 hot gas defrosting Principal diagram R717 CO2 brine system CO2 as a refrigerant in industrial systems Continued2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=9http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=9RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 9 Article CO2 refrigerant for industrial refrigeration R717, R 404A, R 134a, . . . . . . CO2 Pump circulating system DX system 30C 86F 12C 10F 7C 19F 7C 19F 20C 4F Figure 10 Principal diagram CO2 cascade system with 2 temperature levels e. g. supermarket refrigeration Figure 9 shows a low temperature refrigerating system 40C 40F using CO2 as a brine system with ammonia on the highpressure side. The CO2 system is a pump circulating system, where the liquid CO2 is pumped from the receiver to the evaporator. Here it is partly evaporated, before it returns to the receiver. The evaporated CO2 is then condensed in the CO2 NH3 heat exchanger. The heat exchanger acts as an evaporator in the NH3 system. Figure 10 shows a mixed system with ooded and DXsystem, e. g. for a refrigeration system in a supermarket, where 2 temperature levels are required When determining the design pressure for CO2 systems, the two most important factors to consider are Pressure during stand still Pressure required during defrosting Importantly, without any pressure control, at stand still, i. e. , when the system is turned o, the system pressure will increase due to heat gain from the ambient air. If the temperature were to reach 0C 32F, the pressure would be 34. 9 bar 505 psi or 57. 2 bar 830 psi 20C 68F. For industrial refrigeration systems, it would be quite expensive to design a system that can withstand the equalizing pressure i. e. , saturation pressure corresponding to the ambient temperature during stand still. Therefore, installing a small auxiliary condensing unit is a common way to limit the maximum pressure during stand still to a reasonable level, e. g. , 30 bar 435 psi. Design pressure With CO2, many dierent ways of defrosting can be applied e. g. , natural, water, electrical, hot gas. Hot gas defrosting is the most ecient, especially at low temperatures, but also demands the highest pressure. With a design pressure of 52 barg 754 psig, it is possible to reach a defrosting temperature of approx. 10C 50F. The saturated pressure at 10C 50F is 45 bar 652 psi. By adding 10 for the safety valves and approximately 5 for pressure peaks, the indicated maximum allowable working pressure would be 52 barg 754 psig gure 11 12. CO2 as a refrigerant in industrial systems Continued2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=10http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=1010 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration Design pressure Continued Figure 11 Practical limit PS Psaturated 15 Design pressure Pressure peaks5 Saturated pressure10Safety valve Figure 12 20 290 30 435 40 580 50 725 60 870 30 22 20 4 10 14 0 32 10 50 20 C 68 F Design temperature 52 bar 754 psi 25 bar 363 psi Saturated pressurep bara psia p 10 barg psig Design pressure p 15 barg psig Design pressure temperature for CO2 bar psi Design pressure 40 bar 580 psi CO2 is an odourless, colourless substance classied as a nonammable and nontoxic refrigerant, but even though all the properties seem very positive, CO2 also has some disadvantages. Due to the fact that CO2 is odourless, it is not self alarming, if leaks occur, ref. 6. CO2 is heavier than air, which means that it falls to the oor. This can create dangerous situations, especially in pits or conned spaces. CO2 can displace oxygen to a point when it is fatal. The relative density of CO2 is 1. 529 air1 0C 32F. This risk requires special attention during design and operation. Leak detection and or emergency ventilation are obvious equipment. Compared to ammonia, CO2 is a safer refrigerant. The TLV threshold limit value is the maximum Safetyconcentration of vapour CO2 in air, which can be tolerated over an eighthour shift for 40 hours a week. The TLV safety limit is for Ammonia 25 ppm and for CO2 5000 ppm 0. 5. Approx. 0. 04 CO2 is present in the Air. With higher concentration, some adverse reactions are reported 2 50 increase in breath rate 3 100 increase in breath rate 5 300 increase in breath rate 810 The natural bodys respiration is disrupted, and breathing becomes almost impossible. Headache, dizziness, sweating and disorientation. 10 Can lead to loss of consciousness and death. 30 Quickly leads to death. 2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=11http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=11RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 11 Article CO2 refrigerant for industrial refrigeration In CO2 NH3 cascade systems it is necessary to use a heat exchanger. Introducing exchangers creates a loss in the system eciency, due to the necessity of having a temperature dierence between the uids. However, compressors Eciencyrunning with CO2 have a better eciency and heat transfer is greater. The overall eciency of a CO2 NH3 cascade system is not reduced when compared to a traditional NH3 system gure 13 ref. 3. COPcoefficient of refrigerant system performance 1, 75 1, 921, 771, 86 2, 18 1, 09 1, 38 1, 22 1, 42 1, 78 0 0, 5 1 1, 5 2 2, 5 Ammonia, single stage Ammonia, two stages R22, single stage R22, two stage Ammonia CO2 cascade system COP Source IIAR Albuquerque, New Mexico 2003, P. S Nielsen T. Lund Introducing a New Ammonia CO2Cascade Concept for Large Fishing Vessels 40 25C 40 77F 50 25C 58 77F Figure 13 Example In CO2 systems with traditional refrigeration compressors, both miscible and immiscible oil types are used table 2. For immiscible lubricants, such as polyalphaolen PAO, the lubricant management system is relatively complicated. The density of PAO is lower than the density of the liquid CO2. Thus the lubricant oats on top of the refrigerant, making it more dicult to remove than in ammonia systems. Also, to avoid fouling evaporators, the compressor oil separation with non miscible oils must be highly eective basically, a virtually oil free system is desirable. Oil in CO2 systems With miscible lubricants, such as polyol ester POE, the oil management system can be much simpler. POE oils have high anity with water, so the challenge when using POE is to ensure the stability of the lubricant. In volatile brine systems using CO2 as a secondary refrigerant, and in recirculating systems with oil free compressors, no oil is present in the circulated CO2. From an eciency point of view, this is optimum because it results in good heat transfer coecients in the evaporators. However, it requires that all valves, controls and other components can operate dry. CO2 and oil Oil type PAO Polyalphaolen oil Synthetic Mineral oil POE Polyolester oil Ester oil Solobility Low immiscible High miscible Hydrolysis Low High anity to water Oil separation system Special demand High ltration demanded Multistage coalescing lters Active carbon lter No special requirements System requirements like HCFCHFC Oil return system Special demand Oil drain from low temperature receiver oil density lower than CO2 opposite NH3 Simple System requirements like HCFCHFC Challenge Oil separation and return system Long term oil accumulation in e. g. evaporators High anity to water Long term stability of oil Clean refrigerant system required Table 22007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=12http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=1212 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration Compared to ammonia and R134a, CO2 diers in many respects. The following comparison illustrates this fact to allow an true comparison, operational conditions, i. e. , evaporating temperature, condensing temperature, are kept constant. Comparison of component requirements in CO2, ammonia and R134a systems Comparison of pipe cross section area Wet return Liquid lines Wet return Liquid Refrigerant R 134a R 717CO2 Capacity k WTR 250 71 250 71 250 71 Wet return line T KF 0. 8 1. 4 0. 8 1. 4 0. 8 1. 4 p barpsi 0. 0212 0. 308 0. 0303 0. 439 0. 2930 4. 249 Velocity msfts 11. 0 36. 2 20. 2 66. 2 8. 2 26. 9 Diameter mminch 215 8. 5 133 5. 2 69 2. 7 Area Wet return mm2inch2 36385 56. 40 13894 21. 54 3774 5. 85 Liquid line Velocity msfts 0. 8 2. 6 0. 8 2. 6 0. 8 2. 6 Diameter mminch 61 2. 4 36 1. 4 58 2. 3 Area liquid mm2inch2 2968 4. 6 998 1. 55 2609 4. 04 Total pipe cross section area Area Wet return mm2inch2 39353 61. 0 14892 23. 08 6382 9. 89 Liquid cross section area 8741 Leqv 50 m 194 ft Pump circ. ncirc 3 Evaporating temp. TE 40C 40F Table 3 Comparison of pipe cross section area Dry suction Liquid lines Dry suction Liquid Refrigerant R 134a R 717CO2 Capacity k WTR 250 71 250 71 250 71 Dry suction line T KF 0. 8 1. 4 0. 8 1. 4 0. 8 1. 4 p barpsi 0. 0212 0. 308 0. 0303 0. 439 0. 2930 4. 249 Velocity msfts 20. 4 67 37. 5 123 15. 4 51 Diameter mminch 168 6. 6 102 4. 0 53 2. 1 Area Dry suction mm2inch2 22134 34. 31 8097 12. 55 2242 3. 48 Liquid line Velocity msfts 0. 8 2. 6 0. 8 2. 6 0. 8 2. 6 Diameter mminch 37 1. 5 21 0. 8 35 1. 4 Area liquid mm2inch2 1089 1. 69 353 0. 55 975 1. 51 Total pipe cross section area Area Dry suction liquid mm2inch2 23223 36. 00 8450 13. 10 3217 4. 99 Liquid cross section area 5430 Leqv 50 m 194 ft Evaporating temp. TE 40C 40F Condensing temp. TE 15C 5F Table 42007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=13http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=13RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 13 Article CO2 refrigerant for industrial refrigeration Comparison of pipe cross section area Dry suction Liquid lines Dry suction Liquid Refrigerant R 134a R 717CO2 Capacity k WTR 250 71 250 71 250 71 Dry suction line Area Dry suction mm2inch2 22134 34. 31 8097 12. 55 2242 3. 48 Liquid line Area liquid mm2inch2 1089 1. 69 353 0. 55 975 1. 51 Total pipe cross section area Area Dry suction liquid mm2inch2 23223 36. 00 8450 13. 10 3217 4. 99 Relative cross section area 7. 22. 61. 0 Liquid cross section area 5430 Vapour cross section area 959670 Leqv 50 m 194 ft Evaporating temp. TE 40C 40F Condensing temp. TE 15C 5F 0 1 2 3 4 5 6 7 8 R134a CO2R717 5 95 4 9630 70 Liquid Suction 0 1 2 3 4 5 6 7 8 2 5 95 4 9630 70 Liquid Suction Table 5 Comparison of component requirements in CO2, ammonia and R134a systems Continued Comparison of compressor displacement Compressor Refrigerant R 134a R 717CO2 Refrigerant capacity k WTR 250 71 250 71 250 71 Required compressor displacement m3hft3h 1628 57489 1092 38578 124 4387 Relative displacement 13. 18. 81. 0 Evaporating temp. TE 40C 40F Condensing temp. TE 15C 5F Table 6 Comparison of pressure subcooling produced in liquid risers Refrigerant R 134a R 717CO2 Hight of liquid riser H mft 3 9. 8 3 9. 8 3 9. 8 Pressure produced in liquid riser p barpsi 0. 418 6. 06 0. 213 2. 95 0. 329 4. 77 Subcooling produced in liquid riser t KF 14. 91 26. 8 5. 21 9. 4 0. 88 1. 6 Evaporating temp. TE 40C 40F H CO2reciever H CO2 reciever pt Table 72007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=14http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=1414 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration A comparison of pump circulating systems shows that for wet return lines, CO2 systems require much smaller pipes than ammonia or R134a table 3. In CO2 wet return lines, the allowable pressure drop for an equivalent temperature drop is approximately 10 times higher than Wet return lines in recirculation systems For both recirculating and dry expansion systems, calculated sizes for CO2 liquid lines are much larger than those for ammonia, but only slightly larger than those for R134a table 3 and 4. This can be explained by ammonias much larger latent heat relative to CO2 and R134a. Refer to the tables showing the relative liquid and vapor crosssectional areas for the three refrigerants table 5. The total crosssection area for the CO2 system is approximately 2. 5 times smaller than that of an ammonia system and approximately seven times smaller than that of R134a. This result has interesting implications for the relative installation costs for the three refrigerants. Due to the relative small vapor volume of the CO2 system and large volumetric refrigeration capacity, the CO2 system is relatively sensitive to capacity uctuations. It is therefore important to design the liquid separator with sucient volume to compensate for the small vapor volume in the pipes. for ammonia or R134a wet return lines. This phenomenon is a result of the relatively high density of the CO2 vapor. The above comparison is based on a circulating rate of 3. The result would be slightly dierent if the circulating rate is optimized for each refrigerant. In the comparison of dry suction lines, the results are very nearly the same as in the previous comparison, in terms of both pressure drop and line size table 4. Suction lines in dry expansion systems Liquid lines The required compressor capacity for identical refrigeration loads is calculated for the three refrigerants table 6. As illustrated, the CO2 system requires a much smaller compressor than the ammonia or R134a systems. For compressors of identical displacements, the capacity of the compressor using CO2 is 8. 8 times higher than using ammonia, and 13 times higher than that using R134a. The subcooling produced in a liquid riser of a given height H is calculated for the three refrigerants table 7. The subcooling for the CO2 liquid riser is much smaller than that for ammonia and R134a. This characteristic must be noted when designing CO2 systems to prevent cavitations and other problems with liquid CO2 pumps. In ammonia systems, oil is changed and non condensables are purged frequently to minimize the oil, oxygen, water and solid contaminants that can cause problems. Compared to ammonia systems, CO2 is less sensitive, but if water is present, problems may occur. Some early CO2 installations reported problems with control equipment, among other components. Investigations revealed that many of these problems are caused by water freezing in the system. Modern systems use lter driers Water in CO2 Systemsto maintain water content in the system at an acceptable level. The acceptable level of water in CO2 systems is much lower than with other common refrigerants. The diagram in gure 14 is showing the solubility of water in both liquid and vapor phases of the CO2 liquid and vapor as function of temperature. The solubility in the liquid phase is much higher than in the vapor phase. The solubility in the vapor phase is also known as the dew point. 0 200 400 600 800 1000 1200 6040200204060 Temperature Weight 106 of water weight of refrigerant ppm Liquid CO2 Vapour CO2 o C o F403210476468140 Water solubility in liquid vapour CO2 Figure 142007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=15http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=15RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 15 Article CO2 refrigerant for industrial refrigeration R134a R404A CO20 1000 2000 50301010C Temperature Water solubility in various refrigerants in vapour phase Maximum solubility ppm mgkg R717 Figure 15 Water in CO2 Systems Continued Temperature Liquid Vapour 1 10 100 1000 50301010C Maximum solubility ppm mgkg Water solubility in CO2 Figure 15. 1 Figure 162007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=16http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=1616 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration 0 10 20 30 40 50 60 70 80 90 100 40 40 20 4 0 32 CO2 H2O CO2 ICE CO2 Water vapour phase Temperature 20 C 68 F Water solubility in vapour CO2 Weight 106 of water weight of refrigerant ppm Figure 17 Water in CO2 Systems Continued The diagram in gure 14 is showing that the water solubility in CO2 is much lower than for R134a or ammonia. At 20C 4F, water solubility in the liquid phase is CO2, 20. 8 ppm R134a, 158 ppm Ammonia, 672 ppm Below these levels, water remains dissolved in the refrigerant and does not harm the system. Figure 16 illustrates how water H2O molecules are dissolved if the concentration is lower than the maximum solubility limit, and how the H2O molecules precipitate out of solution into droplets if the water concentration is higher than the maximum solubility limit. If the water is allowed to exceed this limit in a CO2 system, problems may occur, especially if the temperature is below 0C. In this case, the water will freeze, and the ice crystals can block control valves, solenoid valves, lters and other equipment gure 17. This problem is in particular critical in ooded and direct expansion CO2 systems, but not so much in volatile secondary systems because less sensitive equipment is used. It is important to notice, that the below mentioned reactions with water dont take place in a wellmaintained CO2 system, where the water contents is below the maximum solubility limit. In a closed system such as a refrigeration system, CO2 can react with oil, oxygen, and water, especially at elevated temperatures and pressures. For example, if the water content is allowed to rise above the maximum solubility limit, CO2 can form carbonic acid, as follows ref. 4 and 5. Chemical reactions CO2 H2O H2CO3 CO2 water carbonic acid In CO2 production systems, where water concentrations can rise to high levels, it is well known that carbonic acid can be quite corrosive to several kinds of metals, but this reaction does not take place in a wellmaintained CO2 system, because the water content in the system is kept below the maximum solubility limit. If the water concentration is relatively high, CO2 and water in vapor phase can react to form a CO2 gas hydrate. CO2 8 H20 CO2H208 CO2 water hydrated CO2 Water in Vapor Phase The CO2 gas hydrate is a large molecule and can exist above 0C 32F. It can create problems in control equipment and lters, similar to the problems that ice can make. Generally, esters such as POE react with water as follows RCOOR H2O ROH RCOOH ester water alcohol organic acid POE lubricant As shown, if water is present, POE will react with water to form alcohol and an organic acid carboxylic acid, which is relatively strong and may corrode the metals in the system. Thus, it is very important to limit the water concentration in CO2 systems if POE lubricants are used. 2RCH3 3 O2 2 H202 2RCOOH oil oxygen water acid PAO lubricant PAO lubricant is also called synthetic mineral oil. Ordinarily, PAO is very stable. However, if sucient free oxygen is present, such as might be available from corrosion in pipes, the oxygen will react with the lubricant, and form carboxylic acid. 2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=17http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=17RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 17 Article CO2 refrigerant for industrial refrigeration Controlling the water content in a refrigeration system is a very ecient methode to prevent the abovementioned chemical reactions. In Freon systems, lter driers are commonly used to remove water, usually the type with a zeolite core. The zeolite has extremely small pores, and acts like a molecular sieve gure 18. Removing water Water molecules are small enough to penetrate the sieve, and being very polar, are adsorbed inside the zeolite molecules. R134a molecules are too large to penetrate the sieve. When the replaceable core is removed, the water goes with it. Figure 18 CO2receiver RH 100RH 22 n 1n 3 RH 15. 4 1 ppm Example 4010C CO2pump circulating system with 20 ppm water Max. solubility in liquid CO2 40C 130 ppm 10C 405 ppm Max solubility in vapour CO2 40C 7 ppm 10C 33 ppm RH 15. 4 20 ppm RH 0. 25 1 ppm CO2 Compressor NH3Compressor CO2 receiver CO2NH3 Figure 18. 12007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=18http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=1818 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration Figure 18. 2 Removing water Continued Principlediagram CO2NH3cascadesystem CO2Evaporator Liquid CO2reciever CO2Compressor Dry suction CO2 NH3heat exchanger Filter drier Moisture indicator Filter driers installed in bypasslines or main liquid line Liquid Filter drier Moisture indicator Figure 19 CO2 is a nonpolar molecule, so the removal process is dierent. Like water molecules, CO2 molecules are small enough to penetrate the molecular sieve. However, the water molecules adsorbed onto the molecular sieve act in such as way as to kick out the CO2 molecule, due to the dierence in polarity. Zeolite lter driers cannot be used in ammonia systems, because both water and ammonia are very polar. Even though the driers function dierently in this respect in CO2 systems, the eciency is fairly good. The water retention capacity is approximately the same as in R134a systems. The most eective location to detect and remove water is where the concentration is high. The solubility of vaporphase water in CO2 is much lower than in the liquid phase. Therefore, a greater amount of water can be transported in liquid lines. Fig. 18. 1 illustrates the variation of the relative humidity in a pump circulation system operating at 40C. The illustration shows that the relative humidity is highest in the wet return line, and that it is depending on the circulating rate. In a DX system the variation of the relative humidity diers, but also in this case the highest concentration is located in the suction line g. 18. 2. Taking advantage of this principle, moisture indicators and lter driers are typically installed in a liquid line or liquid bypass line from the receiver gure 19. The moisture level indicated by these devices varies according to temperature and also by type of indicator. In gure 20, the indication level of a Danfoss SGN indicator is shown for liquid CO2. Example 4010C CO2DX system with 20 ppm water Max. solubility in liquid CO2 40C 130 ppm 10C 405 ppm Max solubility in vapour CO2 40C 7 ppm 10C 33 ppm RH 66. 7 20 ppm RH 4. 9 1 ppm Compressor NH3Compressor NH3 RH 100 20 ppm Dry suction Heat exchanger condenser Liquid Evaporator2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=19http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=19RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 19 Article CO2 refrigerant for industrial refrigeration Figure 20 Removing water Continued Unlike in some ammonia systems, the pressure in CO2 systems is always above atmospheric. However, water can still nd its way into CO2 systems. Water may contaminate a CO2 system through ve dierent mechanisms 1. Diusion 2. Maintenance and repair practices 3. Incomplete water removal during installation commissioning 4. Watercontaminated lubricant charged into the system 5. Watercontaminated CO2 charged into the system Obviously, all these mechanisms should be avoidedminimized. How does water enter a CO2 system To illustrate a scenario in which water may contaminate a system, think of a contractor, who, believing CO2 is a very safe refrigerant, thinks that it may be handled without following the normal ammonia safety requirements. He might open up the system to perform a repair. Once the system is opened up, air enters, and the moisture in the air condenses inside the piping. If he does not evacuate the system very thoroughly, some water may well be retained. In another scenario, our contractor forgets that the lubricant used in the system, POE, has a high anity for water, and leaves the cap o the container. After charging the POE into the system, the water may begin to cause mischief within the system. 2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=20http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=2020 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration 50 solid CO2 at the triple point Liquid 20 bar 290 psi 78. 4C 109. 1F 56. 6C 69. 9F 5. 2 bara 75. 1 psia 31C 87. 9F 1450 100 145 10 14. 5 1 psi bar Pressure Enthalpy JFigure 22 If the set pressure of a safety valve in the vapor phase is 50 bar 725 psi, e. g. , the centerline, the relief line pressure will pass the triple point and 3 of the CO2 will change into solid as it continues to relieve. In a worstcase scenario e. g. , a long relief line with many bends, solid CO2 may block this line. The most ecient solution to this problem would be to mount the safety valve without an outlet line, and relieve the system directly to the atmosphere. The phase change of the CO2 does not take place in the valve, but just after the valve, in this case, in the atmosphere. If a pressure relief valve is set to relieve liquid at 20 bar 290 psi, the relief products would pass through the triple point, whereupon 50 of the CO2 would change into solid upon further relief, subjecting the relief line to a high risk of blockage. Thus, to safely protect liquid lines against formation of dry ice, connect safety relief valves to a point in the system at a pressure higher than the triple point pressure of 5. 2 bar 75. 1 psi. CO2s particularly high triple point can cause solid CO2 to form under certain conditions. Figure 21 shows the expansion processes occurring in pressure relief valves starting at three dierent conditions. If the set pressure of a pressure relief Miscellaneous features to be taking into consideration in CO2 refrigeration systems Safety valve valve in the vapor phase is 35 bar 507 psi or less, e. g. , the rightmost line, the pressure in the relief line will pass through the triple point at 5. 2 bar 75. 1 psi. Once below the triple point, the CO2 will be pure vapor. Figure 21 CO2 expansion phase changes Safety valves CO2 expansion phase changes Cleaning lers charging CO2 50 solid CO2 at the triple point Liquid 20 bar 290 psi 78. 4C 109. 1F 56. 6C 69. 9F 5. 2 bara 75. 1 psia 31C 87. 9F Vapour 50 bar 725 psi Vapour 35 bar 507 psi 0 solid CO2 at the triple point 3 solid CO2 at the triple point 1450100 14510 14. 51 psibar Pressure Enthalpy J2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=21http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=21RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 21 Article CO2 refrigerant for industrial refrigeration It is important to start up with CO2 in the vapor phase, and continue, until the pressure has reached 5. 2 bar 75. 1 psi. Thus, it is strongly recommended to write a procedure for charging a CO2 system. One must be aware when charging a refrigerant system that until the pressure reaches the triple point, the CO2 can only exist Charging CO2as a solid or vapor inside the refrigeration system. Also, the system will exhibit very low temperatures until the pressure is suciently raised gure 22. For example, at 1 bar 14. 5 psi, the sublimation temperature will be 78. 4C 109F. Filter cleaning The same phenomenon applies also when cleaning liquid strainerslters. Even though CO2 is nontoxic, one cannot just drain the liquid outside the system. Once the liquid CO2 contacts the atmosphere, the liquid phase will partly change into the solid phase, and the temperature will drop dramatically, as in the example described above. Thus sudden temperature drop is a thermal shock to the system materials, and can cause mechanical defects in the materials. Such a procedure would be considered to be a code violation because this equipment is not normally designed for such low temperatures. Trapped liquid is a potential safety risk in refrigerant systems, and must always be avoided. This risk is even higher for CO2 systems than for ammonia or R134a systems. The diagram in gure 23 are showing the relative liquid volume Trapped liquidchange for the three refrigerants. As shown, liquid CO2 expands much more than ammonia and R134a, especially when the temperature approaches CO2s critical point. 0 10 20 30 40 50 60 70 80 90 100 2002040 Temperature Volume change CO2 R134a R717 Relativ liquid volume Reference 40 o C o F o C 32104468o F 20 0 20 40 o C 40 4 32 68 104 o F Temperature 40 Figure 23 The most critical leak in a CO2 NH3 cascade system is in the heat exchangers between CO2 and NH3. The pressure of the CO2 will be higher than the NH3, so the leak will occur into the NH3 system, which will become contaminated. CO2 2 NH3 H2NCOONH4CO2 ammonia ammonium carbamate Leaks in CO2 NH3 cascade systems The solid substance ammonium carbamate is formed immediately when CO2 is in contact with NH3. Ammonium carbamate is corrosive ref. 5. 2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=22http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=2222 RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 RA Marketing. 09. 2007. mwa Article CO2 refrigerant for industrial refrigeration CO2 is compatible with almost all common metallic materials, unlike NH3. There are no restrictions from a compatibility point of view, when using copper or brass. The compatibility of CO2 and polymers is much more complex. Because CO2 is a very inert and stable substance, the chemical reaction with polymers is not critical. The main concern with CO2 is the physiochemical eects, such as permeation, swelling and the generation of cavities and internal fractures. These eects are connected with the solubility and diusivity of CO2 in the actual material. Danfoss has carried out a number of tests to ensure that components released for use with CO2 can withstand the impact of CO2 in all aspects. Material compatibility The tests have shown that CO2 is dierent, and modications have to be made on some products. The large amount of CO2, which can dissolve in polymers, has to be taken into consideration. Some commonly used polymers are not compatible with CO2, and others require dierent xing methods e. g. sealing materials. When the pressure is close to the critical pressure and the temperature is high, the impact on polymers is much more extreme. However, those conditions are not important for industrial refrigeration, as pressure and temperatures are lower for these systems. CO2 has good properties, in particular at low temperature, but it is not a substitution for ammonia. The most common industrial CO2 refrigeration systems, is hybrid systems with ammonia on the high temperature side of the system. CO2 is in many aspects a very uncomplicated refrigerant, but it is important to realize that CO2 has some unique features compared with other common refrigerants. Knowing the dierences, and taking these into account during design, installation, commissioning and operation, will help avoid problems. Conclusion The availability of components for industrial CO2 refrigeration systems with pressures up to approximately 40 bar is good. Several manufacturers of equipment for traditional refrigerants can also supply some components for CO2 systems. The availability of components for the higher pressure industrial CO2 refrigeration systems is limited, and the availability of critical components is an important factor in the growth rate of CO2 application. 1 Bondinus, William S ASHRAE Journal April 1999 2 Lorentzen, Gustav, Reprint from IIR Conference 1994 Proceedings New Applications of Natural Working Fluids in Refrigeration and Air Condition 3 P. S Nielsen T. Lund IIAR Albuquerque, New Mexico 2003, Introducing a New Ammonia CO2Cascade Concept for Large Fishing Vessels 4 Broesby Olsen, Finn Laboratory of Physical Chemisty, Danfoss AS International Symposium on HCFC Alternative Refrigerants. Kobe 19981998 IIF IIR Commission B1, B2 and E2, Purdue University 5 Broesby Olsen, Finn Laboratory of Physical Chemisty, Danfoss AS IIF IIR Commissions B1, B2, E1 and E2 Aarhus Denmark 1996 6 Io R. Safety Code for Refrigeration Systems Utilizing Carbon Dioxide The Institute of Refrigeration. 2003. 7 Vestergaard N. P. IIAR Orlando 2004. CO2 in subcritical Refrigeration Systems 8 Vestergaard N. P. RAC refrigeration and air condition magazine, January 2004. Getting to grips with carbon dioxide. References2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=23http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=23RA Marketing. 09. 2007. mwa RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242 23 Article CO2 refrigerant for industrial refrigeration2007-09-12T07:50:13+02:00http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=24http://danfoss.ipapercms.dk/refrigerationandairconditioning/RA/DanfossIndustrialRefrigeration/CO2Refrigerant/?Page=24RZ0ZR202 DKRCI. PZ. 000. C1. 02 520H2242Produced by Danfoss RA Marketing, mwa. 092007 The Danfoss product range for the refrigeration and air conditioning industry Danfoss Refrigeration Air Conditioning is a worldwide manufacturer with a leading position in industrial, commercial and supermarket refrigeration as well as air conditioning and climate solutions. We focus on our core business of making quality products, components and systems that enhance performance and reduce total life cycle costs the key to major savings. Controls for Commercial Refrigeration Controls for Industrial Refrigeration Industrial Automation Household Compressors Commercial Compressors Thermostats Sub Assemblies Electronic Controls Sensors We are oering a single source for one of the widest ranges of innovative refrigeration and air conditioning components and systems in the world. And, we back technical solutions with business solution to help your company reduce costs, streamline processes and achieve your business goals. 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